1. Field of the Invention
This invention relates to a blade member of tungsten carbide (WC) based cemented carbide for cutting tools, which has a superior heat plastic deformation resistance and, accordingly, which displays superior cutting performance for a long period of time when the blade member is used for high-speed cutting accompanied with high heat-generation at the cutting edge, and heavy duty cutting such as high-feed cutting and deep cutting.
2. Prior Art
Japanese Patent Unexamined Publication Nos. 52-110209 based cemented carbide having a WC-based cemented carbide substrate and a hard coating deposited thereon. The cemented carbide substrate has the following composition in terms of weight % (hereinafter % indicates % by weight):
one, or two or more of cobalt (Co), nickel (Ni) and iron (Fe) as a binder-phase forming component: 5% to 15%,
one or more of carbides, nitrides and carbo-nitrides of metals in Groups IV.sub.A, V.sub.A and VI.sub.A of the Periodic Table, as a dispersed-phase forming component: 5% to 40%, and
the remainder: WC and unavoidable impurities.
The surface portion of the cemented-carbide substrate includes a surface softening layer in which a Co-pool phase is formed. The hard coating is formed by the use of a standard chemical vapor deposition method or physical vapor deposition method, and comprises a single layer of one of, or a plurality of layers of two or more of carbides, nitrides, carbo-nitrides, boro-nitrides, oxy-carbides, oxy-nitrides and oxy-carbo-nitrides of the same metals in Groups IV.sub.A, V.sub.A and VI.sub.A as well as aluminum (Al) oxides, having an average layer thickness of 2 .mu.m to 20 .mu.m.
In the surface-coated blade member of WC-based cemented carbide, as disclosed in Japanese Patent Unexamined Application No. 53-131909, the cemented carbide substrate is manufactured by heat treatment of a vacuum-sintered body, in a carburizing atmosphere of CH.sub.4 +H.sub.2 maintained at a temperature of no less than 1,400.degree. C. for a predetermined period of time. Further, as disclosed in Japanese Patent Unexamined Application No. 61-34103, the WC-based cemented carbide substrate may be manufactured by sintering under conditions wherein after maintaining the body at a temperature of no less than 1,400.degree. C. in a vacuum of no greater than 10.sup.-1 torr for a predetermined period of time, the atmosphere is switched to the above-described carburizing atmosphere, and the body is cooled from the sintering-completion temperature to a predetermined temperature at a temperature gradient of 0.5.degree. C./min to 2.5.degree. C./min. These substrates are produced by subjecting the ones which are once sintered to treatment in a carburizing atmosphere, and a WC-skeleton is firmly formed by means of sintering. Therefore, with the subsequent treatment in the carburizing atmosphere, there is formed a surface softening layer in which hardness and Co content exhibits a moderate change from the substrate surface inwardly of the substrate, and the Co-pool phase in the surface softening layer presents a form of dispersed lumps.
In cases where the conventional surface-coated blade member made of WC-based cemented carbide is used, particularly for cutting such as high-speed cutting accompanied with high heat generation at the cutting edge, or heavy duty cutting with high feed cutting and deep cutting, plastic deformation occur within a relatively short period of time, terminating the tool life of the blade member.